1. Field of Invention
The present invention relates to a liquid crystal alignment agent, a liquid crystal alignment film and a liquid crystal display element having thereof. More particularly, the present invention relates a liquid crystal alignment agent that has excellent pretilt angle stability, a liquid crystal alignment film formed by the liquid crystal alignment agent, and a liquid crystal display element comprises the liquid crystal alignment film.
2. Description of Related Art
In recent years, there is a requirement of the wide view angle of the liquid crystal display element, thus the requirements of the electrical properties and display properties have become stricter. In wide view angle liquid crystal display element, the vertical alignment liquid crystal display element is widely studied. For meeting better electrical properties and display properties, liquid crystal alignment film becomes one of the important factors.
The liquid crystal alignment film of the vertical alignment liquid crystal display element is used to regularly align the liquid crystal molecules with a larger pretilt angle when the electrical field is not applied. For producing the aforementioned liquid crystal alignment film, a liquid crystal alignment agent having polymers such as polyamic acid or polyimide is firstly coated on a surface of the substrate, being subjected to a thermal treatment and an alignment treatment, thereby obtaining the liquid crystal alignment film.
JP Patent No. 2893671 discloses a polyimide for producing the liquid crystal alignment agent of vertically aligned liquid crystal display element. The polyimide is synthesized by polymerizing a tetracarboxylic dianhydride compound and a diamine compound having a cholesterol skeleton.
The aforementioned liquid crystal alignment film can keep the liquid crystal molecules at 88° to 89° of the high pretilt angle to achieve excellent liquid crystal alignment properties. However, the liquid crystal alignment film still has a defect of lower pretilt angle stability, thereby drastically reducing the display quality of the liquid crystal display element.
Accordingly, there is a need to improve the aforementioned disadvantages for meeting the requirements of the liquid crystal alignment agent.